1. The Field of Art
This invention relates to a process for the non-destructive examination of ferromagnetic bodies or parts of bodies in which is produced a magnetic field whose stray fields extending outside the bodies or parts of bodies are measured by means of magnetic field sensors arranged on or above the surface.
2. Description of the Prior Art
Ferromagnetic bodies are measured non-destructively for structural faults by means of magnetic stray fluxes which, in the event of internal structural faults, occur outside the body surfaces due to stationary magnetic fields produced in the bodies. The stray fluxes are detected by magnetic field sensors arranged on or close to the body surfaces. An apparatus for non-destructive examination of ferromagnetic bodies has been described, for example, in DE-PS No. 3 132 808.
When the surface of bodies takes an irregular course, more powerful magnetic stray fields occur outside the body in the regions of these irregularities, e.g. at the edges and corners, and the magnitude of these fields frequently exceeds that of stray fields produced by structural faults in the interior of body sections which have a regular surface. Examination by means of magnetic stray fields has therefore hitherto been limited to bodies or body sections on which the surface takes a regular course and different methods of examining faults have been employed in the regions of edges, corners or ends of bodies. For example, these regions have been investigated for structural faults by means of magnetic powder testing or the color penetration test. Since these methods entail a visual control of the test sample, they are relatively time consuming and expensive.
It is an object of the present invention to develop a process for the non-destructive examination of ferromagnetic bodies having sections of surface adjoining along edges and/or at corners by which the detection of structural faults by means of the measurement of magnetic stray fields could also be carried out in the regions of the edges and/or corners.